Optical measurement device, method for revising optical measurement device, and optical measurement method

ABSTRACT

Provided is an optical measurement device configured so that a high-accuracy three-dimensional image can be obtained. An emission angle of a ray of light is changed in such a manner that the rotation frequencies of two motors configured to rotatably drive a first optical path changing unit and a second optical path changing unit is controlled. The ray of light is emitted to a front three-dimensional region, and reflected light is obtained. Then, calculation is made by a computer, and in this manner, three-dimensional data on a measurement target object is obtained. The amount (vibration amount) of axial backlash or play of a rotary mechanism, such as a motor shaft, along which the ray of light is emitted is measured in real time, and such a backlash or play amount is subtracted from a three-dimensional image obtained by the computer. Consequently, a high-accuracy three-dimensional image is obtained.

TECHNICAL FIELD

The present invention relates to an optical measurement deviceconfigured such that an optical sensor is inserted into a deep hole of ameasurement target object such as a mechanical component tothree-dimensionally capture reflected light for observation andmeasurement of geometric accuracy of a deep hole bottom portion, such asdimensions and flatness.

BACKGROUND ART

For example, finished dimensions, the level of geometric accuracy, andthe like for a cylinder or a fuel injection nozzle of an automobileengine greatly influence power performance and a fuel consumptionefficiency of an automobile. For testing, a contact-type measurementmachine such as a roundness measurement machine or a surface roughnessmeter has been generally used. However, in recent years, an opticalnon-contact-type measurement machine has been introduced for the purposeof not damaging a measurement target object.

A unit configured to obtain shape data on an inner surface of themeasurement target object in a non-contact state employs, for example,the image diagnosis technique (the optical imaging technique) ofthree-dimensionally emitting laser light and capturing interfering lightfrom reflected light, thereby performing numerical processing for athree-dimensional shape by a general method such as a heterodyne methodto measure the geometric accuracy.

In a medical field, a method for providing an observable tomographicimage of an affected area of an inner portion of a human body, such asX-ray CT, magnetic resonance imaging, and an optical coherencetomography (OCT) image for emitting far-red light with excellentpermeability and capturing reflected light to fetch, utilizing coherencyof light, numerical data on a three-dimensional shape, has been studiedand utilized.

A representative structure of an observation device employing thetechnique of irradiating an inner peripheral surface of a mechanicaldevice or a mechanical component with a ray of light to observe ormeasure the inner surface is as described in Patent Literatures 1 to 3,for example.

In an OCT endoscope described in Patent Literature 1, rotation force ofa motor is, as illustrated in FIG. 8 of this literature, transmitted toa rotary shaft through a belt, and is further transmitted to a lens unitthrough a flexible shaft including, e.g., an optical fiber passingthrough the inside of a tube-shaped optical sheath. However, in thisconfiguration, a two-dimensional tomographic image illustrated in FIG.26 of this literature can be obtained, but no three-dimensional imagecan be obtained.

An OCT endoscope described in Patent Literature 2 employs an OCTthree-dimensional image system. In this system, an elongated tube-shapedcatheter is inserted into an annular guide catheter illustrated in FIG.1 of this literature, and the catheter includes an optically-connectedrotatable and slidable optical fiber or core. A body tissue isirradiated in such a manner that the optical fiber is rotated whilebeing moved in a length direction as illustrated in FIG. 3 of thisliterature, and an analysis image is observed. However, in thisconfiguration, there is a problem that abrasion powder is caused due tofriction between an inner peripheral surface of the catheter and anouter peripheral surface of a drive shaft. Moreover, due to friction,warpage, torsion, and the like of the drive shaft, an uneven rotationspeed, a delay in rotation transmission, torque loss fluctuation, andthe like are caused. For these reasons, the resultant analysis image isdistorted, and required accuracy for spatial resolution and definitioncannot be obtained.

A technique described in Patent Literature 3 employs an endoscope. Inthe endoscope, a motor (7, 8) respectively rotates a sheath tube (5, 6)and a wedge prism (3, 4). In this manner, an emission light raydirection is changed forward so that a portion to be observed uponintravital observation can be freely changed.

However, in this configuration, the rotation frequencies of the twomotors are not synchronized with each other, and no rotation detectionpulse from the motors is utilized. For these reasons, only a change inthe light ray direction can be performed. Thus, a ray of light cannot beemitted in a spiral pattern. For this reason, a three-dimensional imagecannot be obtained by capturing and calculation of reflected light fromthe front by a computer. Moreover, the sheath tube is rotatable, butrotation backlash or play (e.g., 10 microns) in an axial direction (alongitudinal direction) is allowed. For this reason, the sheath tuberotates while vibrating in the axial direction. A distance between asensor unit and a testing target is changed by the distance of thebacklash or play. For this reason, an accurate distance to the testingtarget cannot be measured, and image definition is low.

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: Japanese Patent No. 3885114-   PATENT LITERATURE 2: Japanese Patent No. 4520993-   PATENT LITERATURE 3: JP-A-2002-550

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made in view of the above-describedtypical situation, and an object of the present invention is to providean optical measurement device configured to obtain a high-accuracythree-dimensional image in the following manner: a ray of light isemitted forward in, e.g., a spiral pattern according to programming, andthen, the captured reflected light is used for a computer to fetch athree-dimensional shape; and the amount (a slight distance) of axialbacklash or play of a rotary body configured to emit the ray of light isdetected and subtracted.

Solution to the Problems

According to one technique for solving the above-described problems, inan optical measurement device configured to three-dimensionally emit aray of light from a tip end side of a probe to obtain athree-dimensional image, the probe includes a translucent referenceplate, a plurality of motors, and a rotary-side optical fiber and/or anoptical path changing unit rotatable together with a rotary shaft ofeach motor, and the probe has a displacement detection unit configuredto detect slight displacement of each rotary shaft in an axial directionthereof.

Effects of the Invention

According to the present invention, an optical measurement device can beprovided, which is configured to detect the amount (slight distance) ofaxial backlash or play of a rotary scanning mechanism configured to emita ray of light and subtract such an amount from collectedthree-dimensional image data, thereby accurately obtaining ahigh-accuracy three-dimensional image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a main portion of an optical probeaccording to an embodiment of an optical measurement device of thepresent invention.

FIG. 2 is a view of a configuration of the optical measurement device ofthe present invention.

FIG. 3 is a view for describing scanning of a deep hole by the opticalprobe of the optical measurement device of the present invention.

FIG. 4 is a view for describing a rotation pulse generation section of afirst motor of the optical probe of the optical measurement device ofthe present invention.

FIG. 5 is a view for describing a rotation pulse generation section of asecond motor of the optical probe of the optical measurement device ofthe present invention.

FIG. 6 is a view for describing operation of the optical probe of theoptical measurement device of the present invention.

FIG. 7 is a view for describing operation of the optical probe of theoptical measurement device of the present invention.

FIG. 8 is a view for describing operation of the optical probe of theoptical measurement device of the present invention.

FIG. 9 is a view for describing an emission area of the optical probe ofthe optical measurement device of the present invention.

FIG. 10 is a view for describing a three-dimensional scanning area ofthe optical probe of the optical measurement device of the presentinvention.

FIG. 11 is a timing chart of operation of the optical probe of theoptical measurement device of the present invention.

FIG. 12 is a view for describing operation of the optical probe of theoptical measurement device of the present invention.

FIG. 13 is a view for describing the emission area of the optical probeof the optical measurement device of the present invention.

FIG. 14 is a graph of data obtained when there is no vibration of theoptical measurement device of the present invention.

FIG. 15 is a graph of data obtained when there is vibration of theoptical measurement device of the present invention.

FIG. 16 is a view for describing lengths measured for the opticalmeasurement device of the present invention upon revision.

FIG. 17 is a view for describing lengths measured for the opticalmeasurement device of the present invention upon measurement.

DESCRIPTION OF THE EMBODIMENTS

A first feature of an optical measurement device of the presentembodiment is that in an optical measurement device configured tothree-dimensionally emit a ray of light from a tip end side of a probeto obtain a three-dimensional image, the probe includes a translucentreference plate, a plurality of motors, and a rotary-side optical fiberand/or an optical path changing unit rotatable together with a rotaryshaft of each motor, and the probe has a displacement detection unitconfigured to detect slight displacement of each rotary shaft in anaxial direction thereof.

According to this configuration, rotation vibration of the motors can bedetected in real time, and a measurement error due to backlash of arotary scanning section can be corrected. This leads to high-accuracymeasurement.

A second feature is that the displacement detection unit of the opticalmeasurement device uses, as a reference value, preset three-dimensionalposition information on the translucent reference plate, i.e.,three-dimensional information on a distance to each point of thetranslucent reference plate, and detects, as a displacement, adifference between an actual measurement value of measured distance dataobtained during rotation of each motor and the preset reference value.

With this configuration, the amount of backlash or vibration in theaxial direction can be, in real time, removed from shape data on atesting target object bottom surface by a simple configuration, leadingto accurate and precise measurement of accuracy of the hole bottomsurface.

A third feature is that an exterior of a main body of the probe of theoptical measurement device is a tube, and a first motor and a secondmotor are arranged in the tube. The optical path changing unit includesa first optical path changing unit configured to rotate together with arotary shaft of the first motor, and a second optical path changing unitconfigured to rotate together with a rotary shaft of the second motor. Astationary-side optical fiber is built in the tube, and thestationary-side optical fiber and the rotary-side optical fiber areoptically connected together through a rotary optical connector. Thefirst optical path changing unit is positioned on a tip end side of thestationary-side optical fiber, and is rotatably driven by the firstmotor such that the ray of light is rotatably emitted forward with anangle with respect to a rotation center. The second optical pathchanging unit is integrally disposed on a tip end side of therotary-side optical fiber, is positioned between the stationary-sideoptical fiber and the first optical path changing unit, and is rotatablydriven by the second motor such that the ray of light is rotatablyemitted with an optical path being inclined with a slight angle withrespect to the rotation center and the first optical path unit isirradiated with the ray of light. The ray of light is transmitted fromthe stationary-side optical fiber through the rotary optical connector,the second optical path changing unit, and the first optical pathchanging unit in this order, and then, is emitted forward.

According to this configuration, backlash and rotation vibration of thefirst and second motors in the axial direction can be detected in realtime, and the measurement error due to backlash of the rotary scanningsection can be corrected. This leads to high-accuracy measurement.

A fourth feature is that a first pulse generation unit configured togenerate at least one or more pulses in a single rotation according tothe rotation angle of the first motor, and a second pulse generationunit configured to generate at least one or more pulses in a singlerotation according to the rotation angle of the second motor areincluded. A control unit configured to adjust the rotation speeds of thefirst and second motors based on the pulses from the first and secondpulse generation units is included. By rotation made such that arelationship between the rotation speed N1 of the first motor and therotation speed N2 of the second motor satisfies N2=N1−X[rotations/second], the ray of light is emitted forward from the firstoptical path changing unit at the rotation speed N1 [rotations/second],and the emission angle of the ray of light with respect to the rotationcenter is changed at a speed X [rounds/second].

According to this configuration, the ray of light can be emitted forwardacross a wide area depending on a combination of the rotation angles ofthe first and second optical path changing units.

A fifth feature lies in the method for revising the optical measurementdevice having the above-mentioned features. Specifically, a revisionblock formed of, e.g., a flat plate is disposed at the front of theprobe of the optical measurement device. When a ray of light isthree-dimensionally emitted during rotation of the probe, aninter-target distance T is T=(D2−L2), and a value Ls as Ls=(Ds−T) isused as a reference value of the translucent reference plate, where foreach point, a given true distance to the revision block is Ds, apre-revised measurement value by the probe is D2, and a measureddistance to the reference plate is L2.

By this revision method, an absolute reference for measurement andcorrection is obtained, and therefore, high-accuracy measurement can beperformed using the optical measurement device.

A sixth feature lies in an optical measurement method forthree-dimensionally emitting a ray of light to obtain athree-dimensional image. Specifically, the ray of light is emitted to atesting target (a measurement target object) through a translucentreference plate while the direction of the ray of light is being changedby driving an optical path changing unit. Then, a signal on a measureddistance to the translucent reference plate and a signal on a measureddistance to the testing target are obtained from reflected light.Subsequently, a difference between the value of the signal on themeasured distance to the testing target and a preset reference value asthree-dimensional distance information is used as a displacement, and inthis manner, the measured distance to the testing target is corrected.

According to this measurement method, a measurement error can becorrected, leading to high-accuracy three-dimensional measurement.

EMBODIMENT

Next, a preferable embodiment of the present invention will be describedwith reference to the drawings.

FIGS. 1 to 15 illustrate an embodiment of an optical measurement deviceof the present invention.

FIG. 1 is a sectional view of an optical probe of the opticalmeasurement device of the embodiment of the present invention, and astationary-side optical fiber 1 configured to guide a ray of light froma back end side to a tip end side of the probe is inserted into thesubstantially center of a sufficiently-long tube (a catheter) 6.

A rotary-side optical fiber 2 is rotatably provided on a tip end side ofthe stationary-side optical fiber 1. On a tip end side of therotary-side optical fiber 2, a first optical path changing unit 3including, e.g., a lens or a prism in such a shape that both surfaces ofa substantially circular columnar transparent body are cut alongsubstantially flat surfaces not parallel to each other is, independentlyof the rotary-side optical fiber 2, attached to rotate by a first motor12. It is configured such that the ray of light is, by rotation of thefirst optical path changing unit 3, rotatably emitted forward with anangle of θ1+θ2 with respect to an axis in the figure, for example.

A second optical path changing unit 20 configured to collect the ray oflight having transmitted through the stationary-side optical fiber 1 andto rotatably emit the ray of light to the first optical path changingunit 3 with a slight angle (θ1) with respect to the axis is attached toa tip end of the rotary-side optical fiber 2. In FIG. 1, the secondoptical path changing unit 20 is formed of a combination of a conicalcollecting lens 20 c and a prism 20 d, for example.

The rotary-side optical fiber 2 and the stationary-side optical fiber 1have end surfaces processed to the right angle, and face each other witha slight distance of about 5 μm. Including a rotary light shieldingplate 5 and an optical fiber fixture 4, the rotary-side optical fiber 2and the stationary-side optical fiber 1 form a rotary optical connector22. A high transmittance is maintained between the rotary-side opticalfiber 2 and the stationary-side optical fiber 1, and the rotary-sideoptical fiber 2 and the stationary-side optical fiber 1 are opticallyconnected together with little loss.

The first motor 12 is built in the tube 6, and a rotor magnet 11 isattached such that a hollow rotary shaft 10 supported by first bearings9 a, 9 b rotates. In the first motor 12, voltage is, through an electricwire 23, applied to a motor coil 7 attached to the inside of a motorcase 8. The first optical path changing unit 3 is rotatable with thefirst optical path changing unit 3 being integrally attached to a holderportion 10 a of the hollow rotary shaft 10.

In a second motor 19, a second rotary shaft 13 supported by secondbearings 18 a, 18 b is, with light pressure, fitted into a hole openingat the substantially center of a vibrator 14, and stable friction forcebetween the vibrator 14 and the second rotary shaft 13 is generated byelasticity or spring properties of the vibrator 14. The second rotaryshaft 13 of the second motor 19 is fixed to a center hole of therotary-side optical fiber 2. Voltage is applied to a pattern electrode16 and an electrostrictive element 15 through a provided electric wire17, and therefore, the second optical path changing unit 20 is rotated.Rotation of the vibrator 14 relative to the motor case 8 is restricted,and the electric wire 17 functions as an anti-rotation lock in the caseof the simplest structure. Needless to say, the second motor may be amotor including the same rotor magnet and coil as those of the firstmotor, and the first motor may be a motor including the same vibrator asthat of the second motor.

The first motor 12 is provided with a first pulse generation unit 25including a rotary member 25 a and a stationary member 25 b asillustrated in FIG. 4. Similarly, the second motor 19 is provided with asecond pulse generation unit 24 including a rotary member 24 a and astationary member 24 b as illustrated in FIG. 5. Each of these units isconfigured to generate a single pulse signal or multiple pulse signalsper rotation according to rotation of a corresponding one of the firstand second motors. For these pulse generation principles, a magneticsensor such as an induction coil or a Hall element or an optical sensorincluding an optical shutter and an optical sensor is used, for example.

In FIG. 1, a translucent reference plate 21 made of a material throughwhich the ray of light can be transmitted, such as glass, quartz, orsapphire, is integrally attached to the tube 6 at the front of the firstoptical path changing unit 3 configured to emit the ray of light. Asnecessary, a flat plate portion 21 a or a substantially sphericalportion is formed at the translucent reference plate 21. The flat plateportion 21 a does not have a constant thickness, but the thickness ofthe flat plate portion 21 a is, as necessary, changed for a lensfunction. Moreover, a coating and the like for reducing surfacereflection and minimizing total reflection of the ray of light toenhance the transmittance is applied to the optical fiber fixture 4 asnecessary.

In the first motor 12 of FIG. 1 in the optical measurement deviceillustrated in FIG. 2, a tip end portion of the tube 6 is, asillustrated in FIG. 3, inserted into a hole 27 of a measurement targetobject 26, and emits the ray of light in a tip end direction 29.

Rotary driving is made by a power supply from a motor driver circuit 86of FIG. 2, and the second motor 19 is rotatably driven by voltageapplication from a second motor driver circuit 87. Moreover, the firstmotor 12 adjusts a rotation speed thereof by the pulse signal from thefirst pulse generation unit 25 illustrated in FIG. 4, and the secondmotor 19 can be adjusted to a preset rotation speed value by the pulsesignal from the second pulse generation unit 24 illustrated in FIG. 5.

Next, characteristic features and advantageous effects of the opticalmeasurement device of FIGS. 1 to 5 mentioned above will be described indetail.

In FIG. 2, a stand 81 on a base 80 is provided with a slider 82configured to move up and down by a slider motor 83. A ray of light suchas far-red light or laser is emitted from a light source in a main body85, and passes through a connection portion 84. Then, the ray of lightis guided into the slider 82, and advances through the stationary-sideoptical fiber 1 in the tube 6.

In FIG. 1, the ray of light passes from the stationary-side opticalfiber 1 to the rotary optical connector 22, and is emitted after havingpassed through the rotary-side optical fiber 2, the second optical pathchanging unit 20, and the first optical path changing unit 3 a in thisorder. The far-red light further passes through the translucentreference plate 21. The ray of light reflected from a surface of themeasurement target object passes, in this order, the translucentreference plate 21, the first optical path changing unit 3 a, the secondoptical path changing unit 20 a, the rotary-side optical fiber 2, therotary optical connector 22, and the stationary-side optical fiber 1 inthe opposite direction of the above-described optical path, and then, isguided to an optical coherence analysis section 88 of FIG. 2.

In FIGS. 12 and 13, the ray of light is emitted to a bottom portion ofthe deep hole 27 of the measurement target object 26. In this manner,digital data on the three-dimensional shape of a surface 27 a is fetchedfor measurement of geometric accuracy of the bottom portion of the holeand observation on the presence or absence of an internal defect bymeans of a three-dimensional image.

In FIG. 1, power is supplied through the electric wire 23, and the firstmotor 12 rotates at a constant speed within a range of about 900 to20,000 rpm. The ray of light guided from the stationary-side opticalfiber 1 passes through the rotary optical connector 22 and therotary-side optical fiber 2, and then, is emitted from the secondoptical path changing unit 20 a. The ray of light is reflected on thesubstantially flat surface of the first optical path changing unit 3 a,and changes its direction to a direction with a certain angle (adownward direction with an angle of θ1+θ2 as indicated by an arrow inFIG. 1). In this manner, the ray of light is rotatably emitted. In thisstate, the angle α1 of the first pulse generation unit 25 of the firstmotor 12 of FIG. 4 is zero degree, and the angle α2 of the second pulsegeneration unit 24 of the second motor 19 of FIG. 5 is also zero degree.A phase difference between these two angles is 0 degree, where the phasedifference is represented by (α1−α2).

In this state, a light ray emission direction is greatly bent withrespect to the axis, and an emission angle is in the downward directionwith (θ1+θ2).

Next, when the first optical path changing unit 3 and the second opticalpath changing unit 20 rotate at the same rotation speed and move topositions which are 180 degrees opposite to those of FIG. 1 as indicatedby 3 b and 20 b in the figure, the ray of light is, as illustrated inFIG. 6, rotatably emitted as follows: the ray of light is emitted fromthe second optical path changing unit 20 b, and is reflected on thesubstantially flat surface of the first optical path changing unit 3 bsuch that the direction of the ray of light is changed to a directionwith a certain angle (an upward direction with an angle of θ1+θ2 asindicated by an arrow in FIG. 6). In this state, the angle α1 of thefirst pulse generation unit 24 of the first motor 12 is 180 degrees, andthe angle α2 of the second pulse generation unit 24 of the second motor19 is also 180 degrees. A phase difference (α1−α2) between these twoangles is 0 degree as in FIG. 6. In this state, the light ray emissiondirection is greatly belt with respect to the axis, and the emissionangle is in the upward direction with (θ1+θ2).

In FIG. 6, the angle Q of the substantially flat surface of the firstoptical path changing unit 3 b and the angle S of a surface of the prism20 d of the second optical path changing unit 20 are set such that thesesurfaces are not parallel to each other and that, e.g., an angle of 5degrees or more is formed between these surfaces. This is because theresultant three-dimensional image data might be degraded due to totalreflection of the ray of light when the above-described surfaces areparallel to each other. As long as it is designed such that the firstand second optical path changing units are not parallel to each otherwith the rotation angle phase difference (α1−α2) between the first andsecond optical path changing units being zero degree, a favorable imagecan be obtained in any state without concerns on parallelization of thefirst and second optical path changing units. Note that in FIGS. 6 to 8,the translucent reference plate forms a hemispherical surface, but maybe a flat plate.

Next, FIG. 7 illustrates a state when the phase angle is changed in sucha manner that the rotation speeds of the first optical path changingunit 3 a and the second optical path changing unit 20 a aredifferentiated from each other.

In FIG. 7, the ray of light emitted from the second optical pathchanging unit 20 b with an angle with respect to the axis is reflectedon the substantially flat surface of the first optical path changingunit 3 a, and changes its direction to the opposite angle direction. Asa result, the ray of light is rotatably emitted substantially inparallel to the axis substantially on the axis. In this state, the angleα1 of the first pulse generation unit 25 of the first motor 12 is zerodegree, and the angle α2 of the second pulse generation unit 24 of thesecond motor 19 is −180 degrees due to a delay in rotation. A phasedifference (α1−α2) between these two angles is +180 degrees. In thisstate, the light ray emission angle is (θ1+θ2)≈zero degree.

Next, FIG. 8 illustrates a state when the first optical path changingunit 3 a and the second optical path changing unit 20 a have rotated,with the same rotation frequency, to positions which are 180 degreesopposite to those in the state of FIG. 7.

In FIG. 8, the ray of light emitted from the second optical pathchanging unit 20 a with an angle with respect to the axis is reflectedon the substantially flat surface of the first optical path changingunit 3 b, and changes its direction to the opposite angle direction. Asa result, the ray of light is rotatably emitted substantially inparallel to the axis substantially on the axis. In this state, the angleα1 of the first pulse generation unit 25 of the first motor 12 is 180degrees, and the angle α2 of the second pulse generation unit 24 of thesecond motor 19 is zero degree due to a delay in rotation. A phasedifference (α1−α2) between these two angles is +180 degrees. In thisstate, the light ray emission angle is also (θ1+θ2)≈zero degree as inFIG. 6.

FIG. 9 illustrates, as viewed in a plane, the rotation phase angle(α1−α2) and the forward light ray emission direction as described withreference to FIGS. 1 to 8. An irradiation direction changes due to thephase difference (α1−α2) between the angle α1 of the first pulsegeneration unit 25 of the first motor 12 and the angle α2 of the secondpulse generation unit 24 of the second motor 19, and the ray of light isemitted forward across a front area indicated by a radius R in thefigure.

FIG. 10 is a view three-dimensionally showing the light ray emissionarea. The ray of light is adjusted such that focusing is made within anarea of about five millimeters about a position at the front L of thetube 6. Thus, the ray of light is emitted in a substantially conicalshape with an angle of (θ1+θ2) in the area with the radius R in thefigure, and three-dimensionally scans the target object.

FIG. 11 is a generated pulse timing chart for the first motor 12 and thesecond motor 19 of the probe for optical imaging according to thepresent invention. An upper diagram in the figure shows the pulsesgenerated from the first pulse generation unit 25 of the first motor 12,and a lower diagram in the figure shows the pulses generated from thesecond pulse generation unit 24 of the second motor 19. The horizontalaxis is a time axis.

A time period indicated by “Stand by” in the figure is in such a statethat the first motor 12 and the second motor 19 rotate with the samerotation frequency while waiting for a scanning start signal.

Next, when the Start signal is output by operation of an operator of theoptical measurement device and the optical probe as illustrated in FIGS.1 and 2, the first motor 12 simultaneously rotates at a speed (e.g., 30rotations/second) in terms of, e.g., N pulses/second, thereby beginningstoring, in a computer 89, digital observation image data on themeasurement target object.

At the same time, the second motor 19 rotates at a speed (e.g., 29rotations/second) in terms of, e.g., (N−1) pulses/second. Thus, as shownin the figure, the emission angle changes from θ1 to θ2 in 0.5 seconds,and changes back to the angle θ1 again after a lapse of one second. Inthis manner, three-dimensional light ray emission is completed.

In this case, the computer fetches, in total of two times (two in oneset), three-dimensional data within the time of changing the emissionangle back and forth between θ1 and θ2 in a single round, therebyobtaining clear three-dimensional image data without a gap. When thedata is fetched and stored, the first motor 12 and the second motor 19are brought into the Stand by state again, and rotate while waiting fora subsequent Start signal.

More practical use of the optical measurement device of the presentinvention is as follows, for example. A three-dimensional image isfetched by the computer 89, taking, as a trigger, a moment at which thepulse signal from the first pulse generation unit 25, 25 a, 25 billustrated in FIG. 4 and the pulse signal from the second pulsegeneration unit 24, 24 a, 24 b illustrated in FIG. 5 are both outputsimultaneously. Then, such an image is displayed on a monitor 90.

In the present embodiment, the stationary-side optical fiber 1 does notrotate, in the long tube 6, across the entire length from the back tothe tip end of the tube 6, and therefore, is not fractioned against thetube 6. This can prevent, e.g., a delay in rotation transmission and atorque loss. Moreover, the rotary-side optical fiber 2 is rotatablydisposed in a hole of the hollow rotary shaft 10, leading to no slidingloss. Thus, uneven rotation of the first motor 12 is much less caused.On a typical evaluation scale for rotation speed performance, a rotationangle is represented by percentage. In the present invention, a highperformance of 0.01% has been achieved.

On the other hand, a typical endoscope probe with friction of an opticalfiber has provided only performance with uneven rotation which is morethan about 100 times worse than that of the present invention.

The most important performance required for the optical measurementdevice illustrated in FIGS. 1, 2, 12, and 13 is that thethree-dimensional image is obtained and that the geometric accuracyobtained from the digital three-dimensional image data, such as flatnessof the deep hole bottom portion of the measurement target object, isenhanced. Factors for variation in measurement of the geometric accuracyinclude, for example, backlash or vibration of the rotary shaft of thefirst motor 12 in an axial direction, runout accuracy of the hollowrotary shaft 10 in a radial direction, and accuracy and surfaceroughness of the first optical path changing unit 3 and the secondoptical path changing unit 20. Among these factors, slight displacementdue to backlash or vibration of the first motor 12 in the axialdirection has the greatest influence.

In FIG. 12, when the optical measurement device detects a signal Lmshowing a distance to the bottom portion of the deep hole 27 of themeasurement target object 26, no backlash or vibration of the rotaryshafts 10, 13 of the first and second motors 12, 19 in the axialdirection is caused. When the resultant data of FIG. 14 shows achangeless straight line of a signal Ls showing a measured distance tothe translucent reference plate, there is no error or noise in the waveform of the detected Lm and the measured distance, and therefore, Lmindicates a true numerical value.

However, when backlash or vibration of the rotary shafts 10, 13 of thefirst and second motors 12, 19 of FIG. 12 is caused, the signal Lsshowing the measured distance to the translucent reference plate mightnot show a changeless straight line due to backlash or vibration in theaxial direction. In this case, the distance equivalent to the signal Lsis added to the waveform of Lm showing the detected distance to thetarget object, leading to non-smooth measurement data. For this reason,when (Signal Lm−Signal Ls) is obtained, smooth and accurate data can beobtained as shown in revised data in the figure.

FIG. 13 is for describing a far-red light irradiation area. After thefar-red light has passed through the translucent reference plate 21, theentirety of an inner bottom surface of the measurement target object 26is irradiated with the far-red light. The amount of backlash orvibration of the first and second motors in the axial direction isdetected from the measured distance (signal) Lm to the measurementtarget object and the waveform or change amount of the measured distance(signal) Ls to the translucent reference plate 21. Then, the measureddistance (signal) Lm is corrected.

In this state, the method for determining, upon revision, a referencevalue of the measured distance (signal) Ls to correct the measureddistance (signal) Lm and a state upon measurement will be specificallydescribed with reference to FIGS. 16 and 17.

FIG. 16 is a view for describing each measured dimension upon revision,and FIG. 17 is a view for describing each measurement.

In FIG. 16,

Ds: a given true distance to a revision block 30;

D2: a pre-revised measurement value of each point by the probe; and

L2: a measured distance to the translucent reference plate 21,

-   -   Inter-target Distance: T, T=(D2−L2), and    -   Reference Value of Translucent Reference Plate: Ls, Ls=(Ds−T)

In FIG. 17,

L2: a measured distance to the translucent reference plate 21;

D2: a measured distance to the measurement target object 26;

Corrected True Value to Measurement Target Object 26: D,D=Ls+(D2−L2)=Ls+T, or

Displacement in Axial Direction: (Ls−L2); and

Corrected True Value D: D=D2−(L2−Ls)

The value of Ls for each point of the translucent reference plate 21 isstored in a memory in advance by revision. Upon measurement, D2 and L2are simultaneously measured so that the corrected value D can beobtained according to the above-described expression.

That is, when the distance to the translucent reference plate 21 is,using the ray of light, three-dimensionally measured, a differencebetween the reference value obtained in a revision process and thedistance to the translucent reference plate upon actual measurementindicates the slight displacement (backlash, vibration) of the entiretyof the motor portion in the axial direction. In a specific correctionmethod, the reference value Ls indicating a reference position at eachpoint of the translucent reference plate 21 illustrated in FIG. 16 isobtained in advance in the revision process. Next, upon actualmeasurement, the true value D, i.e., D=D2−(L2−Ls), is obtained in such amanner that the displacement (Ls−L2) in the axial direction issubtracted from the distance measurement value D2 to each point of themeasurement target object 26 of FIG. 17. This algorithm of correctionand detection of displacement of the translucent reference plateprovided at the front is employed as a displacement detection unit. Thetrue value to each point of the measurement target object 26 asdescribed above is combined to create accurate three-dimensional data onthe computer.

In the optical measurement device of the present embodiment, thedisplacement includes three values of backlash of the first motor 12 inthe axial direction, backlash of the second motor 19 in the axialdirection, and an axial component of vibration of other rotary portions.The displacement detection unit is configured to detect the total ofthese three values.

According to the present invention, axial backlash and rotationvibration of the first motor or the second motor can be detected in realtime as described above, and a measurement error due to runout of arotary scanning section can be corrected. Thus, measurement can be madewith high accuracy. Moreover, the amount of backlash or vibration in theaxial direction can be detected from the waveform or change amount ofthe measured distance (signal) Ls to the translucent reference plate 21.

INDUSTRIAL APPLICABILITY

The optical measurement device of the present invention is configured toirradiate, with a ray of light, an inner bottom portion of an automobileengine spray nozzle having a deep hole or a slide bearing having asmall-diameter hole so that a three-dimensional shape observation imagecan be obtained and that geometric accuracy such as bottom portiondimensions and flatness can be accurately measured. Specifically,utilization in industrial and medical measurement devices and testingdevices is expected.

LIST OF REFERENCE NUMERALS

-   1, 31 Stationary-side optical fiber-   2 Rotary-side optical fiber-   3, 3 a, 3 b First optical path changing unit (prism or lens)-   4 Optical fiber fixture-   5 Light shielding plate-   6 Tube (catheter)-   7 Motor coil-   8 Motor case-   9 a, 9 b First bearing-   10 Hollow rotary shaft-   10 a Holder portion-   11 Rotor magnet-   12 First motor-   13 Second rotary shaft-   14 Vibrator-   15 Electrostrictive element-   16 Pattern electrode-   17, 23 Electric wire-   18 a, 18 b Second bearing-   19 Second motor-   20, 20 a, 20 b Second optical path changing unit-   20 c Collecting lens-   20 d Prism-   21 Translucent reference plate-   21 a Flat plate portion-   22 Rotary optical connector-   24, 24 a, 24 b Second pulse generation unit-   25, 25 a, 25 b First pulse generation unit-   26 Measurement target object-   27 Deep hole-   29 Scanning area-   30 Revision block-   80 Base-   81 Stand-   82 Slider-   83 Slider motor-   84 Connection portion-   85 Main body-   86 First motor driver circuit-   87 Second motor driver circuit-   88 Optical coherence analysis section-   89 Computer-   90 Monitor

1. An optical measurement device configured to three-dimensionally emita ray of light from a tip end side of a probe to obtain athree-dimensional image, wherein the probe includes a translucentreference plate, a plurality of motors, and a rotary-side optical fiberand/or an optical path changing unit rotatable together with a rotaryshaft of each motor, and the probe has a displacement detection unitconfigured to detect slight displacement of each rotary shaft in anaxial direction thereof.
 2. The optical measurement device according toclaim 1, wherein the displacement detection unit uses, as a referencevalue, preset three-dimensional information on a distance to thetranslucent reference plate, and detects, as a displacement, adifference between an actual measurement value of measured distance dataobtained during rotation of each motor and the preset reference value.3. The optical measurement device according to claim 1, wherein anexterior of a main body of the probe is a tube, the motors include afirst motor and a second motor, the optical path changing unit includesa first optical path changing unit configured to rotate together with arotary shaft of the first motor, and a second optical path changing unitconfigured to rotate together with a rotary shaft of the second motor, astationary-side optical fiber is built in the tube, the stationary-sideoptical fiber and the rotary-side optical fiber are optically connectedtogether through a rotary optical connector, the first optical pathchanging unit is positioned on a tip end side of the stationary-sideoptical fiber, and is rotatably driven by the first motor such that theray of light is rotatably emitted forward with an angle with respect toa rotation center, the second optical path changing unit is integrallydisposed on a tip end side of the rotary-side optical fiber, positionedbetween the stationary-side optical fiber and the first optical pathchanging unit, and rotatably driven by the second motor such that theray of light is rotatably emitted with an optical path being inclinedwith a slight angle with respect to the rotation center and the firstoptical path changing unit is irradiated with the ray of light, and theray of light is transmitted from the stationary-side optical fiberthrough the rotary optical connector, the second optical path changingunit, and the first optical path changing unit in this order, and then,is emitted forward.
 4. The optical measurement device according to claim3, comprising: a first pulse generation unit configured to generate atleast one or more pulses in a single rotation according to a rotationangle of the first motor; a second pulse generation unit configured togenerate at least one or more pulses in a single rotation according to arotation angle of the second motor; and a control unit configured toadjust rotation speeds of the first and second motors based on thepulses from the first and second pulse generation units, wherein byrotation made such that a relationship between the rotation speed N1 ofthe first motor and the rotation speed N2 of the second motor satisfiesN2=N1−X [rotations/second], the ray of light is emitted forward from thefirst optical path changing unit at the rotation speed N1[rotations/second], and an emission angle of the ray of light withrespect to the rotation center is changed at a speed X [rounds/second].5. A method for revising the optical measurement device according toclaim 1, wherein a revision block formed of, e.g., a flat plate isdisposed at a front of the probe of the optical measurement device, whena ray of light is three-dimensionally emitted during rotation of theprobe, an inter-target distance T is T=(D2−L2), and a value Ls asLs=(Ds−T) is used as a reference value of the translucent referenceplate, where for each point, a given true distance to the revision blockis Ds, a pre-revised measurement value by the probe is D2, and ameasured distance to the reference plate is L2.
 6. A method for revisingthe optical measurement device according to claim 3, wherein a revisionblock formed of, e.g., a flat plate is disposed at a front of the probeof the optical measurement device, when a ray of light isthree-dimensionally emitted during rotation of the probe, aninter-target distance T is T=(D2−L2), and a value Ls as Ls=(Ds−T) isused as a reference value of the translucent reference plate, where foreach point, a given true distance to the revision block is Ds, apre-revised measurement value by the probe is D2, and a measureddistance to the reference plate is L2.
 7. A method for revising theoptical measurement device according to claim 4, wherein a revisionblock formed of, e.g., a flat plate is disposed at a front of the probeof the optical measurement device, when a ray of light isthree-dimensionally emitted during rotation of the probe, aninter-target distance T is T=(D2−L2), and a value Ls as Ls=(Ds−T) isused as a reference value of the translucent reference plate, where foreach point, a given true distance to the revision block is Ds, apre-revised measurement value by the probe is D2, and a measureddistance to the reference plate is L2.
 8. An optical measurement methodfor three-dimensionally emitting a ray of light to obtain athree-dimensional image, comprising: emitting the ray of light to atesting target through a translucent reference plate while a directionof the ray of light is being changed by driving an optical path changingunit; obtaining, from reflected light, a signal on a measured distanceto the translucent reference plate and a signal on a measured distanceto the testing target; and using, as a displacement, a differencebetween a value of the signal on the measured distance to the testingtarget and a preset reference value, thereby correcting the measureddistance to the testing target.